US 2283166 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
* May 19,
W. E. BUELL ETAL METHOD OF TREATING SEWAGE MATERIAL Filed June 25, 1937 L//VE Patented May 19, 1942 METHOD F TREATING SEWAGE MATERIAL Waiter E. Buell ana Leon A. Winter, lsioux city,
, Iowa Application June 23,
treatment similar to ordinary sewage for final disposal.
In order that our invention may be better un-y derstood, we will refer briefly to the characteristics of a trickling filter. `Such a filter generally consists of a bed of coarse material, such as gravel or crushed stone, with which there is associated some means for applying the material to be filtered uniformly over the entire surface of the filter bed. This application means may take the form of the usual stationary spray devices or various known kinds of rotary or traveling distributor devices. In the use of such a filter bed, a gelatinous film forms uponfthe surface of the lter media, which film supports a comparatively heavy growth of active bacterial and plant life which acts upon the sewage in such a manner as to change the form of the dissolved solids and a certain portion of the suspended solids from an objectionable organic material into a more suitable form, whereby the ellluent from the filter is caused to assume a stable condition substantially free from polluting influence. Such a lter bed functions both mechanically and biologically to condition or purify the mate- `rial passing therethrough for nal disposal.
The efficiency of the mechanical operation of the lter may be -determined by the quantity of suspended solids strained out, so to speak, and the biological efciency may "be determined by the quantity of B. O. D, (five-day biochemical oxygen demand) removed by the filter.v Thebiological efficiency of the lter depends upon the condition of the bacterial and plant organisms in the bed, which organisms feed upon the organic material in the sewage. These organisms demand a certain amount of oxygen for their existence, and the requisite amount of oxygen must be supplied in order that they may be properly conditioned to perform their intended functions.
Oxygen may be supplied by causing the sewage material to be applied or dosed to the filter bed in such a way as to provide rest periods during which the flow of the sewage material to the bed is cut of.
Heretofore, according to the usual practice, the
1937, Serial No. 149,880
material to be treated has been received at the treatment plant under variable flow conditions, dependent entirely upon a varying flow from the source, such as a sewer. Such sewage material has been fed to the filter bed, after'primary or i other treatment, in such a way that the rate f flow thereto has been of a variable character and the intervals at which the rest periods occur, vas well as' the duration of such rest periods, have been variable, dependent upon variation in flow of the material from its source to the plant that is, the dosing cycle has varied with variation in flow of the sewage from its source to the plant. These conditionsk have created many disadvantages, including the wasteful necessity of providingand maintaining large land expensive' lter areas, as well as loss in filtering eiciency.
One of the objects of our invention is to provide an improved method of filtering sewage or other waste material, and by which' the disadvantages existent in prior practices are eliminated.
Another object of our invention is to provide a novel manner of handling the feed of sewage Z5 material to a trickling filter, wherein the feed of the material to the filter is not affected by variation in flow of the sewage from its source and wherein the material is applied or dosed to' the filter at a constantly uniform rate'of application, which application is carried on continuously except for interposed periods ofi rest at predetermined intervals and of predetermined y duration. y
Still another object is to providean arrangement by which the rate of application ofthe sewage material to the lter and the liquid and organic loading of the filter may be materially increased with increased filtering efliclency from both mechanical and biological standpoints..
40 An additional Objectis to provide a filter treat'- ment for sewage material whereby the sewagev handling capacity of any given filter area may be increased without increase in size of the filtering area and equipment or any given capacity may be attained by a reduced filter area, all to the end thatv the cost of any given'installation may be reduced by reducing both construction andoperjating costs.
Further objects are to provide an improved manner of sewagetreatment by which the' ny nuisance is eliminated; to provide an improved manner of reoxidation of the lter bed', including the interposing of short rest periods during which the lter bed is drained and air is supplied to the voids formed therein; to provide for an improved biological action in the filter, thereby insuring an improved eluent; to provide a Arate of application of the sewage thereto; and
to provide a sewage treatment of such nature that the effluent finally discharged is of such character that it is substantially free from materials which will cause pollution and so that it is in condition for permissible final discharge.
In practicing our invention, the sewage material is received at the treatment plant at a rate dependent upon the rate of flow of such material from its source. At the treatment plant such material is subject to primary treatment, if it is of such a nature as to require that, and it is finally fed to a filtering zone in which it is subjected to the action of a trickling filter. The
4flow of such material from its source may be of the usual variable nature but, in following our improved method, the flowto the filter zone is controlled in such a way that the material is applied or dosed to such zone at a uniform rate of application during all periods of feed. We have found that the filter bed or zone will best perform its functions if the material is applied thereto at a comparatively high and uniform rate of application and continuously except for short periods of rest interposed at sufficiently frequent intervals and for periods of sufficient duration to accomplish the necessary reoxidation of the filter bed. We provide for that condition by interrupting (or entirely cutting off) the otherwise continuous, uniform, high-rate'feed of material at predetermined times to provide rest periods of sufficient duration to enable the material to drain substantially entirely from the lter bed and to permit the voids formed within the bed to ll with air, after which the same flow at the same uniform rate of application as previously is resumed. We have also found that, in the treatment of certain domestic sewage, for example, excellent results may be obtained by dosing the filter in a controlled, uniform manner at a rate in excess of '7,000,0l00 gallons per acre per day and by providing a total rest period of approximately four minutes during each hour, the rest periods beingcontrolled to occur every thirty minutes for a period of approximately two minutes. The interval of feed between rest periods, as Well as the duration of the rest periods, may be varied, dependent upon the liquid load or organic load imposed upon the filter as t determined by local conditions and by the character of the material being treated. In any event, though, for any particular loading (liquid or organic) and any particular material we, preferably, employ rest periods of uniform duration occurring at predetermined, and preferably uniform, intervals.
Moreparticularly, in carrying out our invention, and to the foregoing end, we may provide a control zone in which there is maintained a predetermined head of material, and from which such material is fed or dosed to the filter zone, The feeding or dosing of the material from the control zone to the filter zone is controlled, independently of the character of the material and the flow of the same, by suitable timing mechanism which positively interrupts the flow of the material from the control zone at predetermined times for a predetermined length of time. In other words, thismechanism controls the time of beginning and ending of the rest period, the duration of which is dependent upon the time required for the material previously flowed to thc filter bed to drain therefrom, which condition, for any particular material being handled, may be determined by observing the discharge of material from the outlet of the filter zone.
In providing a predetermined head condition in the control zone, a problem exists with respect to the disposition and handling of excess material during, for example, maximum or peak flow periods; with respect to insufficiency in flow to maintain the head in the control zone during 10W or minimum flow conditions; and with respect to the disposition of material which continues to flow from the source during the rest period. We take care of these conditions by employing a storage zone in which excess material to be filtered is stored during the high peak flow periods (or periods during which the material flowed is in excess of that required to maintain the predetermined head in the control zone) and during the rest periodsl above mentioned. The storage and control zones may be so related that the storage zone feeds directly to the control zone and such feed is interrupted when the head in the control zone reaches its predeterf mined condition. By so relating the storage and control zones, uniformity in fiow from the control zone under apredetermined head condition is not affected by variation in flow to the storage zone; Wherefore, during rest periods and during periods when the material owed is in excess of vthat required to maintain the head in the control zone, material builds up in the vstorage zone sufficient to maintain the predetermined head condition in the control zone during the minimum flow period or during those periods when the flow of the material is insufficient to maintain the predetermined head in the control zone.
Continuous feeding to or dosing of the filter zone, except for the short periods of rest required for reoxidation purposes, and feeding or dosing at a uniform rate of application, insure an increase in the efficiency of the filter media. Also, by so controlling the flow or dosing action, high rates of application or dosing may be employed over longer periods of time than have heretofore been possible, thereby greatly increasing the capacity of the filter without affecting its efiiciency and intendedA functioning, with the'result that the same amount of sewage handled under usual practice by large filter areas may be handled, in practicing this invention, by filter/areas only a fraction of that previously employed, and with increased efficiency. In order that these results may be accomplished under certain conditions of flow, that is, in order that the flow to the filter Y zone may be maintained at a uniform and high rate of application, we may further include, as an additional step in our method, the return of the eflluent from the filter zone to either the storage or controlzone during the periods of feed in order to maintain a predetermined head and flow condition from the control zone to the filter zone. The return of the filter zone effluent is for only uniformity in fiow maintenance purpose, and it is directly subject to the flow control of the control zone, whereby the rest periods that we definitely impose under the conditions above stated are not in any Way affected by the eluents return, .which takes place only during periods of feed. f
It will be seen from the foregoing that the purpose of the control zone is to accomplish a predetermined rate of application to the lter zone throughout the time that the material is fed or dosed to the filter zone; Vand that the storage in level of material therein. The fiow of material zone, together with the efiiuent return or otherhead maintaining mechanism, or it may take the form of a pump or the like device which operates to feed continuously, during all periods of feed, a uniform amount of material from the storage zone to the filter zone. In the use of a reservoir of the foregoing character, suitable valve mechanism may be actuated under the control of the time-control mechanism to stop and start'the flow of material to the filter zone to begin and end the rest periods; and in the use of a pump, the time-control mechanism may start and stop the pump to provide the rest periods.
In treating certain materials such as, for eX- ample, certain domestic sewage, it may be necessary to first subject the same to so-called primary treatment, in which it is passed through a settling zone before it is fed to the storage zone. Also, in certain instances, itmay be found desirable to pass the effluent from the filter zone into a settling or clarifying zone before passing such eiiluent to the point of final disposal. Independently of these features, however, our invention and discovery essentially involve controlled flow or dosing of the filter zone at a substantially uniform rate of application, and at high rates of application as rated for the'particular sewage or waste material treated over Vlong periods of time, which application is continuous except for the interposing of definite, independently controlled periods of rest of uniform duration determined by the organic characteristics of the sewage or waste material to permit the filter bed to become properly aerated.
Various structural arrangements may be employed in practicing our invention, some of which, for example, are illustrated in the drawing wherein,
Figure 1 is a diagrammatic view showing one form of sewage system embodying our invention;
Fig. 2 is another, and somewhat diagrammatic, view showing another form of structure that may be used in practicing our invention;
Fig. 3 is a wiring diagram illustrating one manner of electrically controlling the flow of material according to our invention;
Fig. 4 is a view diagrammaticaily illustrating another form of structure that may be used-in practicing our invention.
Referring particularly to Fig. 1, the sewage to be treated may be taken directly from a sewer or any other source, and it is eventually flowed through a conduit I to a settling or clarifying tank II at whatever rate it is received from its source. It is to be understood that the settling tank II may be dispensed with, if it is not required for the particular material'treated, withcut departing from our invention. The efliuent from the settling tank H is flowed in an uncontrolled manner through a conduit I 2 to a storage reservoir I3 of sufficient capacity to store and handle any excess material flowed thereto during high peak ow periods and rest periods, which will be referred to further hereinafter.` The storage reservoir I3 is directly connected through a conduit I 4 to a so-called control tank or reservoir I5 which is of comparatively small dimensions and of a shallow nature so as to provide a control that is sensitive to comparatively slight variations from the storage reservoir I3 to the control reservoir I5 is controlled by a valve I6 in conduit I4, which valve is opened and closed by a float I1 as the head or level ofv the material in the tank I5 varies between certainv limits. More particularly, the valve I6 is connected to the float Il' by connections I8 of such a nature that, when thedesired head or level of material is reached in the reservoir I5, the upward movement of the float II to that position will close the valve I6; and, When the level of the material is below that point, the consequent lowering of the float I1 will open the valve I6 and admit material from the reservoir I3 to restore the leveliof the-material in the reservoir I5, at which time the valve I6 is again closed by the float I'I. This cycle is repeated from time tc time as variation in the level of the material inthe reservoir I5 takes place.
The control reservoir I5 is connected by a suitable conduit IQ to a distributor mechanism 20 of the' so-called rotary type, which has distributor arms 2|) that vrotate to discharge the material from the control reservoir I5 upona trickling filter bed 2|. Through the action of the rotary distributor arms 20, the material is distributed in a substantially uniform manner throughout the entire lter bed during all periods ofv feed.
The fiow of the material from the` ontrol reservoir I5 to the filter bedy 2| is' additionally controlled by suitable valve mechanism in such a way as to interrupt the flow and interpose definite periods of rest. v Specifically, a valve 22r is located in conduitIB between the reservoir I5 and the distributor 20. The valve 22 may be opened and closed by means actuated by a solenoid 22B, or opened and closed by a suitable motor or some other power driven means. In order that the periods of rest be interposed at predetermined times independently of the flow of the material to the filter bed, we may employ time clock mechanism 23 of any known form which is adapted to break an electrical circuit at certain predetermined times and for periods of predetermined duration. The time-clock mechanism 23 is, preferably, connected in series with the valve operating mechanism 22a so that, when the clock mechanism functions to break the circuit, the valve 22 is actuated to close the conduity the ow of material I9 and immediately cut ofi to the lter bed 2l. I
One form of electrical circuit that may be employed in controlling the'structure just described is shownin Fig. 3. Specifically, the clock mechanism 23 includes a switch 23a which is closed during periods of feed, thereby closing an electric circuit through wire 24, switch 23?, wires 25 and 26, solenoid 22a -or other suitable operating mechanism, and wires 2l and 28. Duri-.tig this time, the solenoid 22aor other suitable operating mechanism is energized and the' valve 22y is held in its open positionv and the material flows through the conduit I9 to thedistributor 20. The clock vmechanism is constructed and arranged to openfthe switch 23a at a predetermined time and to hold such switch open for that time required for the particular material being treated to drain' from the filter bed 2I. When the switch 23a is opened, the solenoid 22a is de-energized,
thereby closing valve 22 and beginning a definite period cf rest which is continued until the clock mechanism functions to close switch 23a. This.
cycle is continued over and over again to establish definite'aiternating, long periods of feed and short periods of rest. It is to be understood material' flows to the control reservoir I5 and thence, under a constant head, through the conduit I9 to the distributor mechanism 20. The float and valve mechanism I6, I'I is set to maintain a certain uniform flow and rate of application to the filter bed 2l. If the flow to the reservoir I3, as during high peak flow periods, is such as to exceed that predetermined uniform flow and rate of application to the filter bed, the float II will close valve I6, the opening and closing cycle being carried out in such a way as to maintain only a predetermined fiow condition within the reservoir I5 and to the filter bed. The float and valve connection I8 may be adjusted in any desired manner to cause the float I1 to cut off the flow to reservoir I5 at varying liquid levels therein to vary the rate of application of the material to the filter bed 2 I. When the flow is interrupted byt the clock mechanism 23 and when the predetermined level is reached in the reservoir I5, the oncoming material will be stored in the reservoir I3. At the end of each rest period, which period should be long enough to permit the fiuid to substantially entirely drain froi'n the filter bed 2| and allow the voids insaid filter bed to substantially fill 'with air, the clock mechanism 23 functions to again close the switch 2331 thereby opening valve 22;, as above described, and immediately starting the flow of material to the filter bed at the same predetermined and uniform rate that existed prior to the rest period. This cycle is completed over and overagain, with the flow and rest periods alternating at predetermined times and for predetermined periods as determined by the character ofthe material and the liquid and organic loads which the filter is capable of handling.
The effluent from the filter, in the particular arrangement above described, is fed'through a conduit 29 to a clarifying reservoir 30 and thence through a conduit 3| to the point of final dis, posal. In certain cases the fiow characteristics of the material to be filtered may be such that the desired high rate of application cannot be maintained during all periods of feed, and in that event we provide for` the return of the filter efiiuent, or a part thereof, to supplement the material being fed to the controlreservoir I5.
More particularly, the filter discharge conduit f 29 may be connected by suitable conduits 32, 32a and 32b to the control reservoir I5. Or, if desired, this connection may be directly to the storage reservoir I3 or to the flow connections leading to the control reservoir I5. A pump 33 is mounted between the conduits 32a and 32", and it is actuated by an electric motor 33a electrically connected in series with the clock mechanism 23 (see wiring diagram of Fig. 3) so that it may operate only during periods of feed and when the clock switch 23a is in position to close the electric circuit. The operating control of the `pump 33 is further accomplished by a switch 34 adapted to be opened and closed by a float 35 located in the control reservoir I5. With this arrangement. lowering of the level of the material in the reservoir I5 to a predetermined extent (say, for example approximately 1 inch below the level maintained by the float I'I), actuates the switch 34 to close the electric circuit through the clock mechanism 23 and pump 33 to start the pump in operation. A valve 36 is loy level of the material, thereby closing the elee.
trical circuit through wire 24, switch 23, wires 25 and 31, pump motor 33a, wire 38, switch 34 and wire 28, as shown in Fig. 3. When this circuit is closed, the pump 33 is operated to pump filter effluent back through the conduits 32, 32n and 32b to the reservoir I5. The pump 33 will be cut out as soon as the desired level is restored in the reservoir I5, and this cycle will be repeated as often as the lower" g level of the material may cause the same to happen. When the clock mechanism 23 functions to interpose a period of rest, the electric circuit through the motor 33 is opened, regardless of the position of the switch 34, and no effluent is returned from the filter at that time, whereby the filter is permitted to drain in the manner already described.
f If, in the foregoing arrangement, a clarifying ing from conduit 3I to the conduit 32a, to permit selective return of either the filter or clari'- fier effluent, as desired.
Another structural arrangement for carrying out our invention is shown in Fig. 2, which arrangement is shown and described in our co-l pending application Serial No. 61,017, filed January27, 1936, of which this application is a continuation-in-part. This structure is similar to 'that illustrated in Fig. 1 except that the application of the sewage material to the filter is controlled by a pump mechanism adapted to continuously deliver the material to the filter at a constant, uniform rate of application, and the material so delivered to the filter bed is dis- -charged and distributed by stationary spray devices. It will be understood, however, that, if desired, rotary distributor mechanism like that shown inFig. l may be substituted yfor the stationaryl spray devices with results of the character already set forth.
Specifically, the structure shown in Fig. 2 includes a filter bed 40 similar tol the bed 2I (Fig. 1) except that it is provided internally with a plurality of horizontally disposed pipes or ducts 4I at Various heights therein throughout the' mass of the filter medium. These ducts may be made of any suitable material and they may take any desired shape in cross-section, the same being perforated atv the top and Ibottoni sides thereof, providing a multiplicity of openings 42 therein for admitting air to the filter bed. The ends of the air ducts 4I may be connected with the atmosphere in any suitable manner whereby air may freely enter therein without any of the material passing through the filter flowing therefrom.' While these air -ducts-arearranged, `preferab1y,' for a natural flow.` of airy: therethrough -under the iniiuence ofl normal lco'nditions-i-tem'- perature, p ressureor otherwise-existing both outside and within the lter bed, we may ernploy in certain cases mechanical means-fori forcing air into suchA ducts 4and into. the voids formed in the filter bed by thedrainingof the sewage material therefrom, or otherwise. One, such means isillustrated in-Fig.4, whichl-will'be referred to furtherhereinafter. At the bottom .of the filter bed, thereis a drainy `channel 4,3.and the upper side of this ,channel isprov'ided with perforationsv 42 similar tothose inthe air ducts 4| fora similar purpose;y Y f i On the operation of thestructure shownV in Fig. 2, the material to be ltered'maybe fed from a storage reservoirv corresponding to :the reservoir I3 of Fig. 1 through suitable conduit 44 to a control mechanism .and thenceto the lter bed through conduits 46 and". The latter conduit extends-over the upperY surface of the iilter Abed Yand .is provided with a .plurality of stationary nozzles 48-which arel adapted, during the owperiod. to discharge onto the upper surface of the iilter in asubstantially uniform manner throughout the illt'er surface. The control mechanismv may take lany suitable form Y adapted to be cut in at predetermined 'time'sfor pump 33 of Fig. 1, which pumps a continuous uniform amount of material for a storage reservoir to the filter so long as the electric circuit controlling its motor is closed. The time control mechanism may take the form of a time clock 50 similar to the clock 23vof Fig. 1, so disposed in the circuit in which the pump motor is located that -at certain periods it functions to break that circuit and stop the pump 49 and interpose the rest period as in the form of Fig. 1. The electric circuit may include wiring 242/25', 3l', 38' and 28 and clock switch 23' -corresponding to the wiring 24, 25, 3l, 38 and 28 and switch 23* of Fig. 1. Therefore, with structure. ofthe foregoing character, the material to be ltered may be fed in a controlled mannerrit may be fed at a uniform rate of application; the feed of the material to the filter may be stopped and started instantaneously; and the flow may be interrupted at any predetermined time .and for any' taining uniformity in rate of application.' `Other than just described, this form of our invention lizedin tiongff L j Referring to vthe structure shownjin lfigureV 4,(it
mandes 'a nu-.er bedient@ which tnesewage ma yspraynozzles B Ij, Vconteria; .*1s fed by means; duits, 62'63, 'electric pump 64, vand electric time .control mechanism v6 5, the control mechanism `being 1 similarv to thatj` "shownj in Fig. 3. "I'hecondition. They are adequately siippueq :with
the lnecessary amount' ofoxygen requiredffor them'k to: efficiently fperform their puri'cation 20 function with high rates lof application Y or high liquid and organic l loadings over long kperiods f time: Also, the'lter bed,'by the continuous 'applicationat a uniformlfigh rateover long periods of time, is kept inf proper conditionfforf performing its mechanicalfiltering., functions. i1 Clogging and pooling areavoided. The 'nearly"continuous application of the sewage vinaterial"will eliminate 'the y' nuisance due tothe`A fact"*thatY the lter bed is kept wet in a nearly continuous manner, andthe filter flyoes net ex'ist-in-"such vwetted filyterareas. Thesum total lof the `filteringresults,
. both biologically and mechanically, are such that .the efficiency of the filter ismaterially increased While, at the same time, the ltering capacity thereof is greatly increased. The liquid loadings of the filter, as well as the organic loadings therei u of, may be increased far beyond the point of expectation of filter structures operatingv under prior practice. For example, by way of comparison with the usual loadings of the customary or prior filter systems adapted to handle approximately two million gallons per acre per day of the sewage material, the same having an applied strength of approximately 130 P. P. M. of B. O..D.,
or anormal loading -capacityof -250.,pounds per acre-foot per day, in practicing our invention such loadings may be increased at least seven or-eight times and may reach as high as twenty to thirty, or highermillion gallons per acre per day .of the material treated. In any event, while the liquid loadings may vary with organic loadings, our. invention, forbest results compara-- tively with the loading rate of two million gallons of liquid per -acre per day, should be operated at a liquid loading inu excess of seven million gallons per acre per day. Furthermore, in practlcing our invention, through uniformity in rate -of application with very shortrest periods, the
v rate of application, notwithstanding variation in ow from the source, is'smoothed or ironedout in such a way as to avoid ,variations in dosing which reduce total capacity handling ofthe filter structure.. 4 Y
We appreciate..thatthedsagerate or,rate of application of the material to thetlter bed is determined, in part'vat 44le i=.st, byl thebiological capacity ofthe filter.inedillllly but, by -using our invention, any particular` filter structuremay be biologically conditionemfor` handling its full vcapacity at all times with intendedbiological functioning. The rate of applicatflmthe duration of feed, the frequency, of rest'periOdS; ,and theduration of the rest. periods maybe -variedaccording is similar tol that of Fig. 1 andmay wellbel uti- 75- to the organicdoadi-ngf thematerial to be treated. Therefore, one mayfrcadily determine carrying out our novel method of :filtratheleng'th of the feed period and also the frequency and length of the rest periods fromthe characteristics of the material to be treated. For
exa.mple,`in normal operation, a filter operated areathat must be occupied for such filters is considerable vin order to handle the domestic sewage of a city of even comparatively small size.
Our invention greatly relievesvthis condition.-
By stepping up the filtering capacity, the filtering area may be greatly reduced with increased filtering eiilciency, thereby greatly reducing cost from all standpoints. For example, where, according to the vcustomary practice, a filter bed of one acre size may be required to handle the sewage for a particular district, that area may be' reduced to, say, from 116 to 1/4 `of an acre and still more efficiently handle `the same quantity V of sewage.
It is to be understood that, while we have described diiferent-applications of our invention,
other arrangements, embodying the fundamentals and essentials of our invention may be re-l sorted to without departing from the spirit and scope of our invention as defined by the claims that follow.
1. The method of treating sewage or other waste material whichcomprises the steps of: continually feeding the material to be `treated to a trickling filter at a controlled, substantially uniform rate; periodically interrupting the feed to provide intervals of rest; and-timing said periods of feed and rest respectively so that a definite feed period is followed by a definite rest period,
lthe ratio of the period of rest' to the period'of feed (in minutes) 'being approximately 2 to 30'in any given half hour. l
2. The method of treating sewage or other waste material which comprises the steps of: continually feeding the material to be treated to a trickling filter at a controlled, substantially uniform rate; periodically interrupting the feed to provide intervals ofrest; and timing said periods of feed and rest respectively so that a definite feed period is followed by a definite rest period, the ratio of the period of rest to the'period of feed (in minutes) being not lessi-.han 1 ,to 60 nor more than 6 to 60 in any given hour. I
Y WAL'I'ER E. BUELL.'
LEON A. WINTER.